The invention relates to absorption heat pump systems and particularly to liquid/vapor absorption systems using ammonia refrigerant and water, salt, or salt and water absorbents. Thermal efficiencies of such systems have been improved during the past years by use of innovative heat recuperation within the absorber as well as between the one or more absorbers and the generator. Such improvements use absorber heat exchangers as well as generator/absorber heat exchange facilitated by use of the rich or weak absorption working fluid or by separate heat exchange loop. Detailed descriptions on the use and implementation can be found in U.S. Pat. Nos. 4,311,019, 5,024,063, 5,271,235, 5,367,884; R. J. Modahl and F. C. Hayes, "Evaluation of Commercial Advanced Absorption Heat Pump Breadboard", The Trane Company pp. 117-125, 1988, as well as numerous other publications. While all of the above improvements are intended to increase the rating or seasonal thermal efficiency of the absorption system, the use of ammonia, a class 2 refrigerant, prohibits the use of a direct expansion coil in the indoor air handler by safety code and calls for an intermediate coupling loop with an environmentally acceptable and safe fluid for heat transfer, which in turn calls for additional components and reduces the overall efficiency due to pump power consumption and heat transfer inefficiencies.
The prior art ammonia absorption systems reject heat at various components involving at least the condenser and absorber and often also the rectifier/analyzer in the generator unless such rectification is performed by liquid refrigerant feed back rather than a heat exchanger coil as disclosed for example in U.S. Pat. No. 4,106,309. Heat rejection from the ammonia absorption system is obtained by routing the secondary brine through the sorption cycle components rejecting heat, i.e. absorber, condenser and often generator/analyzer. The cooling interface is obtained by routing the secondary brine between the evaporator and the coil extracting heat from the ambient air which is typically the indoor coil in building cooling applications and outdoor coil in building heating applications. As shown and disclosed in "Development of a Residential Gas Fired Absorption Heat Pump", Chemical Section Allied Corporation, August, 1985 and U.S. Pat. No. 5,367,884 switching from heating to cooling can be performed by use of an eight-way valve in the brine/glycol loop, which connects the indoor and outdoor coil with all heat rejecting and heat absorbing components of the sorption cycle. Since one brine must serve both the indoor and outdoor coil under all climate conditions ranging from winter heating at low outdoor temperatures as low as -10.degree. F. or -20.degree. F. to summer cooling at high outdoor temperatures as high as 100.degree. F. to 120.degree. F., such brine not only needs to be designed to be safe to avoid destruction of pumps and coils but also effective as heat transfer fluid over the entire temperature range of operation. The use of the brine itself for thermal communication with the indoor and outdoor coil results in energy efficiency losses due to the additional heat transfer gradients required to move energy into and out of the brine. In addition, brine outdoor heat exchanger coils are larger than those required for direct refrigerant condensation or evaporation and also call for more pressure losses on the air-side of such coils not to mention the pump power requirements to move the brine through the outdoor heat exchanger and all heat rejecting cycle components in the cooling mode or the evaporator in the heating mode.
One of the main challenges for absorption heat pumps is to meet the building load imposed capacity at extreme outdoor temperature conditions. The heat transfer gradients to move energy from and to the brine/glycol increases the required temperature lift between the one or more evaporators and the heat rejecting components of the sorption cycle by about 15.degree. F. to 30.degree. F. thus reducing capacity and efficiency. If operational conditions call for a switch from heating to cooling or vice versa during the operating hours of a day the thermal capacity of the brine/glycol may add to cycling losses.
According to the present invention simplified methods connect and operate liquid/vapor absorption systems comprising at least one evaporator, condenser, absorber and generator with building HVAC indoor and outdoor coils including the use of plumbing and internal heat exchange configurations to reduce the interface of heat exchange between the indoor/outdoor coils and the absorption system to one interface involving the evaporator and only one interface involving either the absorber or condenser for all heat rejection of the absorption system. Such configuration includes the use of heat transfer between at least the absorber and condenser as well as a refrigerant reversing valve to separate the indoor and outdoor coils and loops and to allow for direct refrigerant exposure in the outdoor coil thus eliminating an outdoor brine or glycol loop, elimination of which leads to cost reduction and energy performance enhancement.
The present invention will eliminate the inherent prior art inefficiencies described above by reducing the heat rejection interface between the sorption cycle and the outdoor heat exchanger to one sorption cycle component which in turn allows for use of reversing valve hardware which enables the functional switch of condenser and evaporator and makes it possible to use the refrigerant itself to transfer heat from and to the outdoor coil thus only requiring an intermediate heat transfer loop for the indoor coil, the operating temperature band of which is much narrower which allows for use of a more optimized, less viscous brine than possible if such brine had to serve both indoor and outdoor coils.